Was there really a lone agent within the CIA who refused to let go of the name that finally led to an American SEAL team knocking on Osama Bin Laden's door? I don't know, and neither do you.

But, that agent, dedicating every moment of her career to tracking Bin Laden's rumoured personal courier is the story we were told, and it does translate into a fine film.

After a punishingly long first act, in which a great deal is said, much of it under 'enhanced interrogation', and the threat of third-party torture, the identity of the courier is established, and the hunt can focus on one city in Pakistan. You know how it ends.

Jessica Chastain - neatly stepping in to a role that once would have been Jodie Foster's or Julianne Moore's - makes for a believable, if distractingly young and pretty, agent.

Around her, a very strong support cast bring to life a selection of exactly the -mostly- uber-intelligent alpha males you might expect to populate this story.

Director Kathryn Bigelow (The Hurt Locker) shifts sweetly between the talky, the tense, and the flat-out military. The raid on Bin Laden's compound is outstandingly well done, with a nicely struck balance between the martial and the human.

Zero Dark Thirty is lengthy, finely made, well performed, and credible. By the end I was exhausted, quite moved, and thoroughly satisfied.